The present invention is directed to a hip joint socket for cement-free anchoring in the pelvis, made of plastic material and it includes a socket member with a hemispherical exterior surface which is flattened at its apex region and a socket which is spherical-symmetrical relative to the rotational axis of symmetry of said exterior surface.
For artificial hip joint sockets there is the general requirement for dimensioning the socket to be implanted as a foreign body into the pelvis as small as possible for two reasons. First for limiting the inevitable losses of bone substance and second for reducing the volume of the artifical foreign body to the absolute minimum.
Taking into account these arguments sockets with an approximatively hemispherical shape are to be preferred to those with a conical or cylindrical (note Swiss Pat. No. 566,128) basic shape. Hip joint sockets of the aforementioned type are therefore known for implantation into small, shallow acetabula (note the leaflets from ALLO PRO "Die Huftgelenk-Endoprothese, System Weber-Stuhmer" of 1977 and from AESCULAP 113-C 10 77/4, page 12 "Total-Endoprothesen fur das Huftgelenk").
All these sockets are designed for anchoring with the aid of bone cement. They are not suitable for cement-free implantation having neither an adequate structure of the outer surface, e.g. an exterior thread, nor anchoring pegs or screws for a cement-free fixation, nor can they be clamped into the pelvis.
With a cementfree anchoring the implanted socket is held with a certain prestress in the pelvis. The clamping of the socket member occurs thereby at the lateral surface, i.e. at the equatorial regions. With the aforementioned prior art sockets the clamping effect is prevented due to the flange type rim of the socket.
Furthermore the fixation by clamping is insufficient with these known sockets because theoretically it takes place only along a line in the equatorial plane.